In 2002, there were more than 132,500 multiple births in the United States, the highest number ever recorded. The incidence of multiple births has risen dramatically since 1980, with an 83% increase in twins and more than a 453% increase in triplets and higher-order births (quadruplets and quintuplets). Compared to singletons, infants of multiple births are much more likely to be born early preterm and very low birthweight, important well-documented factors that contribute to their excess morbidity and mortality. In contrast, far less is known about how multiple pregnancies affects the health of the mother. Hospital-based studies report higher rates of preeclampsia, gestational diabetes, PPROM, preterm labor, as well as life threatening complications and maternal admission to intensive care. These studies are limited, though, by their small sample sizes and frequent failure to control for the confounding factors of maternal age and parity. The objective of the study proposed in this application is to fill this knowledge gap by using national vital statistics data to formulate plurality-specific morbidity and mortality risks by maternal age, race, and parity. Three national data sets will be used for this study: the Matched Multiple Birth Data Set for 1995-2000 (for maternal morbidity in twin and triplet pregnancies), the Live Birth Data Set for 1990-2000 (for maternal morbidity in singleton pregnancies), and the Mortality Multiple Cause of Death Data Set for 1990-2000 (for maternal deaths in singleton, twin, and triplet pregnancies), for a study sample of 42,736,904 singleton live births, 322,758 matched sets of twins, 12,133 matched sets of triplets, and 3,580 maternal deaths. Data on an additional 811,929 pregnancies (799,422 singletons, 11,999 twins, and 508 triplets) based on the 2003 revision of the live birth certificate will also be analyzed to determine maternal morbidity and mortality risks by method of conception. The main hypothesis of this proposal is that higher plurality is the predominant factor affecting maternal morbidity and mortality, further potentated by older maternal age and primiparity.